A frequent difficulty in an office or similar environment is communicating with a particular individual when they are not in their office but still in the building. This results not only in "telephone tag" where people continue back-and-forth attempts to return telephone calls, but also in its physical analog where one person visits the office of another, only to find that person to be gone.
One solution to this problem has been the increasingly widespread use of paging receivers, and such devices have become more and more miniaturized. Devices have been constructed, for example, that are the size of a credit card or that are included as part of a watch. Such systems, however, are typically one-way, transmitting only a telephone number, perhaps an additional short numeric code, or possibly a brief alphanumeric message, and are designed for use outside a building.
Within a building, there have been two general directions that system designs have taken. One is the use of radio paging systems within a building, which may be configured to allow receipt of electronic mail messages or to allow users to be notified that they have a call that they can then ask to be transferred to a nearby extension. For example, the Hagl invention (U.S. Pat. No. 5,151,930) transmits the fact of the incoming call and the telephone extension of the calling party by radio to a paging receiver, which indicates to the user that the call has come in and displays the number. The user then locates a telephone instrument and dials a code identifying the user, resulting in the incoming call being transferred to that instrument.
The other direction is the use of automatic personal locating systems that determine where in a building an individual is, and that can automatically route a telephone call to the nearest extension. For example, the Ward invention (U.S. Pat. No. 3,439,320) describes a system that uses ultrasonic sound (using a different frequency for each person) to track the location of individuals in a building so that telephone calls may be routed to them. A number of variations exist using different media. Thus, the Shipley inventions (U.S. Pat. Nos. 4,601,064 and 5,062,151) track the location of individuals that carry devices that repeatedly transmit a digital identifying code via infrared light that is then received by remote sensors installed in individual rooms of a building, with a central computer that polls the remote sensors and determines the location of an individual. Telephone calls can then, if desired, be automatically forwarded to the individual by the PABX system. The individual can, using a switch on the identification device, turn off the forwarding action at a given time if it would be inconvenient.
These approaches have a number of drawbacks. One-way radio paging signals can fail to deliver a messages if the user is in an especially noisy environment, is in a "dead spot" resulting from metal shielding or other interference, or goes outside the range of the transmitter. While these difficulties can be prevented by repeating all transmissions multiple times, this approach does not make efficient use of bandwidth and can also result in considerable delay in receipt of a paging signal or message. One-way communication also does not allow an originator to know whether a message has in fact been received by a user and read, or allow the user to respond. One-way systems that indicate to a user only that a call has come in require the user to find a telephone and dial sufficient digits to cause the call to be transferred, and typically require the caller to be placed on hold during this process, which may be annoying to the caller if the person being paged does not respond or takes a long time to do so.
Systems that automatically track the location of individuals and automatically transfer incoming telephone calls to that location tend to be intrusive, because they necessarily cause a transfer even in circumstances that might be inappropriate (such as transferring a call to an individual who is in an office of someone he or she does not know well or who is in a group meeting that might be disturbed).
The above difficulties are solved by the invention disclosed here (and related inventions) by its provision of both (1) two-way communication and (2) automatic tracking of the location of the individual. This combination allows responses to be sent which are chosen from a set provided with the original message, from a preprogrammed set, or composed by the user. Selection or composition of responses is made easy by use of a thumbwheel that allows display of messages and responses and their choice by pressing a single key (as is described in a copending application). The communication and tracking system also makes possible the transfer of incoming telephone calls remotely by means of selection from a menu.
The present invention provides both two-way communication and tracking by making use of a hybrid communication system with radio used for transmitting data to the user, and infrared light (or, in an alternative embodiment, ultrasonic sound) used for receiving data from the user. This hybrid system makes effective use of the strengths of each form of communication. Radio is used in one direction for broad coverage, ease of implementation, and relative reliability, while infrared light (or ultrasound) is used in the other direction (for acknowledgements, responses, original messages, and location tracking) because of its low power requirements, simplicity of design, small size of the necessary electronics, low cost, and its ability to determine the location of individuals (since infrared light and ultrasonic sound do not pass through walls). Radio is also desirable because its use could allow the design of a paging receiver that works both with conventional paging systems when outside the building and, in addition, with the system described here when inside the building, using the same components.
The use of this hybrid mix of communication media required the design of a communication protocol to fit the characteristics of the two media. The radio medium is characterized by good but not perfect reliability, and moderate to substantial capacity, depending upon availability of particular bands and whether the station is licensed or unlicensed. The system is particularly applicable for use in the recently allocated 1,900 Mhz band for personal communications services for unlicensed use in a building. The infrared medium has somewhat limited capacity in this context because of the need for data to be transmitted repeatedly and because of the need to minimize drain on the battery and to minimize conflict with other nearby communication units. Ultrasound has a naturally low capacity resulting from its susceptibility to interference from echoes as the signal bounces off walls, floor, and ceiling. Both infrared, and, to a lesser extent, ultrasound, have somewhat variable reliability as the user moves from one room to another and as the unit changes position and orientation in that environment. Infrared and ultrasound, are, of course, desirable because they do not easily penetrate walls and ceilings and thus allow reliable identification of the location of the unit.
One example of the requirements for the protocol is illustrated by the fact that unlike more conventional protocols where data is transmitted and an acknowledgement signal is expected immediately if the data has been correctly received, with this protocol data must be sent without waiting for immediate acknowledgement of previous packets, with data broken down into packets with assigned sequence numbers and both data and acknowledgement packets containing the appropriate numbers. This is necessary because with a hybrid system, one direction can be reliable at a time when the other is not, and vice-versa. Other characteristics of the protocol include modifying the rate of repeated transmissions from units and polling to and transmissions from remote stations depending on the probability of expected responses and the user of indicators to signal to the user the status of the communication links, particularly when communication is being impeded.